In a side airbag device described in the following Patent Literature 1, a side airbag is sectioned into a first inflating section (rear bag section) and a second inflating section (front bag section) by a partition wall (front-rear partition) disposed at a position corresponding to a rib region of an occupant in position. An inflator is provided inside the first inflating section, and gas generated from the inflator is supplied through communicating ports formed in the front-rear partition into the front bag section. Through this, the rear bag section is set at a higher pressure than that of the front bag section, thereby securing an initial restraint performance for the occupant in position, and also suppressing influence applied to the occupant even if the occupant is in an inappropriate position (out of position). As the related art of the present invention, the following Patent Literatures 2 to 6 are included, for example.